Objective:To evaluate the clinical efficacy of external therapy with self-made Huatan Prescription combined with conventional western medicine therapy in the treatment of severe pneumonia of phlegm turbidity obstructing lung.Methods:Randomized controlled trial. A total of 114 patients with severe pneumonia of phlegm turbidity obstructing lung in the hospital between July 2020 and December 2021 were enrolled in this study. The patients were divided into two groups by the random number table method, with 57 in each group. On the basis of conventional western medicine therapy, the treatment group was given external therapy of self-made Huatan Prescription, and the control group was given the placebo. Both groups were applied continuously for 5 days. The TCM syndromes were scored before and after treatment. The disease severity was evaluated by Sequential Organ Failure Assessment (SOFA) and Acute Physiology and Chronic Health Evaluation Ⅱ(APACHE Ⅱ). The levels of WBC and procalcitonin (PCT) were detected by automatic blood analyzer. The levels of serum CRP and IL-6 were detected by ELISA. The adverse reactions during treatment were recorded and the clinical efficacy was evaluated.Results:After treatment, the total respinse rate was 92.98% (53/57) in treatment group and was 70.18% (40/57) in control group ( χ2=9.87, P=0.002). The scores of fever, unconsciousness, cough and expectoration, nausea and vomiting, tongue coating and pulse and total score in treatment group were significantly lower than those in the control group ( t=8.95, 7.30, 6.93, 7.37, 12.02, 12.59, 14.29, P<0.01). SOFA (18.12±3.55 vs. 21.46±3.58, t=5.00) and APACHE Ⅱ (13.39±2.72 vs. 16.52±3.13, t=5.70) in treatment group were significantly lower than those in the control group ( P<0.01). The levels of WBC [(11.12±1.61) ×10 9/L vs. (12.69±1.82) ×10 9/L, t=4.88], PCT [(3.72±0.81) μg/L vs. (5.19±0.92) μg/L, t=9.05], serum CRP [(62.09±11.41) mg/L vs. (91.77±15.54) mg/L, t=11.62] and IL-6 [(193.14±32.28) ng/L vs. (235.68±38.75) ng/L, t=6.37] in treatment group were significantly lower than those in the control group ( P<0.01). During treatment, there were no obvious adverse reactions in both groups. Conclusion:Self-made Huatan Prescription external therapy combined with conventional western medicine therapy can improve the clinical symptoms, inhibit the inflammatory response, relieve the disease condition and improve the prognosis of patients with severe pneumonia of phlegm turbidity obstructing lung safely.